Pull `ViewContextProvider` in preview.js

## Feature Description

Refer to the [comment](https://github.com/google/site-kit-wp/pull/11221#discussion_r2248937653) on #11221. `ViewContextProvider` can be pulled into the preview so that we don't have to use it explicitly in individual stories.

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## Acceptance criteria

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## Implementation Brief

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### Test Coverage

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## QA Brief

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## Changelog entry

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Start by reading preview.js and the discussion linked from #11221 to understand how ViewContextProvider is currently used in individual stories. The change is complete when the provider is available from the preview setup and individual stories no longer need to add it explicitly; verify the affected stories and visual regression coverage.

Written by the indexing model from the issue text.